The present invention relates to a piston for an internal combustion engine and more particularly to a piston capable of making shorter the distance that a mixture charge drawn into a combustion chamber so as to flow with a rotational motion about a horizontal axis travels before reaching a spark plug. The present invention further relates to a combustion chamber structure having such a piston.
In a conventional internal combustion engine having a piston reciprocatingly disposed in a cylinder, a mixture charge is drawn from an intake port into a combustion chamber so as flow with a rotational motion about a horizontal axis and ignited by a spark plug after reaching the spark plug or a place adjacent thereto. The term xe2x80x9chorizontalxe2x80x9d is herein used to indicate an axis that transverses or extends across an axis of a combustion chamber.
In order to obtain efficient combustion of a mixture charge drawn into a combustion chamber, it has been proposed, as disclosed in Japanese Patent Provisional Publication No. 9-317555, such a piston that has at a top surface thereof a pair of nearly oval-shaped depressions each located under a pair of intake and exhaust valves. By such depressions, a mixture charge drawn into the combustion chamber from a pair of intake ports can be assuredly formed into a pair of flows that moves with a rotational motion about a horizontal axis.
The piston disclosed by Japanese Patent Provisional Publication No. 9-317555 is advantageous since liquid fuel affixed to the inside of the depressions is removed by the flows efficiently such that formation of deposits on the piston is prevented.
Specifically, in an internal combustion engine having such a piston disclosed by the above-described publication, a mixture charge is drawn from each intake port into the combustion chamber and made to flow with a rotational motion about a horizontal axis in the following manner. Firstly, the mixture charge is made to flow along an inner surface of a cylinder head toward an exhaust valve. From the exhaust valve, the mixture charge is made to flow along an inner surface of a cylinder toward a top surface of a piston. From the top surface of the piston, the mixture charge is made to flow again along the inner surface of the cylinder and then toward the spark plug provided to the cylinder head.
Thus, the distance that the mixture charge travels within the combustion chamber before reaching the spark plug is so long that there is a possibility that when the engine is operated in a high-speed range, the spark plug is ignited before the mixture charge reaches the spark plug or a place adjacent thereto thereby making it impossible to obtain good combustion.
It is accordingly an object of the present invention to provide a piston for an internal combustion engine that is capable of making shorter the distance that a mixture charge drawn from an intake port into a combustion chamber so as to flow with a rotational motion about a horizontal axis travels before reaching a spark plug thereby making it assured to attain good combustion even when the engine is operated in a high-speed range.
It is another object of the present invention to provide a combustion chamber structure for an internal combustion engine having a piston of the foregoing character.
To accomplish the above objects, there is provided according to an aspect of the present invention a piston for an internal combustion engine having a cylinder, a cylinder head closing an end of the cylinder and having an inner surface defining a combustion chamber, a spark plug mounted on the cylinder head, an intake valve mounted on the cylinder head on one of opposite sides of the spark plug and an exhaust valve mounted on the cylinder head on the other of the opposite sides of the spark plug, the piston being reciprocatingly disposed in the cylinder and having at the top surface a cavity for causing a mixture charge drawn into the combustion chamber so as to flow with a rotational motion about a horizontal axis upon opening of the intake valve to flow toward the spark plug.
According to another aspect of the present invention, there is provided a piston for an internal combustion engine having a cylinder, a cylinder head closing an end of the cylinder and having an inner surface defining a combustion chamber, a spark plug mounted on the cylinder head, an intake valve mounted on the cylinder head on one of opposite sides of the spark plug and an exhaust valve mounted on the cylinder head on the other of the opposite sides of the spark plug, the piston being reciprocatingly disposed in the cylinder and having at the top surface a cavity that causes a mixture charge drawn into the combustion chamber so as to flow with a rotational motion about a horizontal axis upon opening of the intake valve to flow upward from a place adjacent a center of the top surface of the piston and toward the spark plug.
According to a further aspect of the present invention, there is provided a combustion chamber structure for an internal combustion engine comprising a cylinder block having a cylinder, a cylinder head closing an end of the cylinder and having an inner surface defining a pentroof-shaped combustion chamber, the inner surface of the cylinder head having a pair of inclined surface sections, at least one intake port formed in one of the inclined surface sections of the cylinder head, at least one exhaust port formed in the other of the inclined surface sections of the cylinder head, and a spark plug disposed between the inclined surface sections of the cylinder head, a mixture charge drawn from the intake port into the combustion chamber being made to flow with a rotational motion about a horizontal axis, and a piston reciprocatingly disposed in the cylinder and having at a top surface thereof a cavity for causing the mixture charge drawn into the combustion chamber to flow toward the spark plug.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.